Journal of the Korean Society for Aeronautical & Space Sciences (한국항공우주학회지)

The Korean Society for Aeronautical and Space Sciences (한국항공우주학회)
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Air Density Measurement in a Narrow Test Section Using a Laser Absorption Spectroscopy

레이저 흡수 분광법을 사용한 좁은 시험 구간 내 공기 밀도 측정

  • Shim, Hanseul (Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology) ;
  • Jung, Sion (Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology) ;
  • Kim, Gyeongrok (Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology) ;
  • Park, Gisu (Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology)
  • Received : 2021.07.01
  • Accepted : 2021.09.27
  • Published : 2021.11.01
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Abstract

In this study, air density in a narrow test section is measured using a laser absorption spectroscopy system that detects oxygen absorption lines. An absorption line pair at 13156.28 and 13156.62 cm-1 are detected. A gas chamber with a height of 40 mm is used as a narrow test section. A triangular spiral-shaped laser path is applied in the gas chamber to amplify absorption strength by extending laser beam path length. A well-known logarithm amplifier and a secondary amplifier are used to electrically amplify absorption signal. An AC-coupling is applied after the logarithm amplifier for signal saturation prevention and noise suppression. Procedure of calculating spectral absorbance from output signal is introduced considering the logarithm amplifier circuit configuration. Air density is determined by fitting the theoretically calculated spectral absorbance to the measured spectral absorbance. Test conditions with room temperature and a pressure range of 10~100 kPa are made in a gas chamber using a Bourdon pressure gauge. It is confirmed that air density in a narrow test section can be measured within a 16 % error through absorption signal amplification using a triangular spiral-shaped beam path and a logarithm amplifier.

본 연구에서는 산소의 흡수선을 검출하는 레이저 흡수 분광 시스템을 사용하여 좁은 시험 구간 내의 공기 밀도가 측정되었다. 13156.28과 13156.62 cm-1에 존재하는 산소의 흡수선 한 쌍이 측정되었다. 높이 40 mm를 가지는 기체 챔버가 좁은 시험 구간으로 사용되었다. 레이저 진행 경로를 확장하여 흡수 세기를 증폭시키기 위해 삼각 나선 형태의 레이저 광경로가 기체 챔버 내에 구성되었다. 잘 알려진 로그 증폭기와 2차 증폭기를 사용하여 흡수선 신호를 전기적으로 증폭하였다. 로그 증폭기 이후 신호 포화 방지 및 노이즈 억제를 위해 AC 커플링이 적용되었다. 로그 증폭기 회로구성을 고려하여 출력 신호로부터 파수별 흡광도를 계산하는 과정이 소개되었다. 이론적으로 계산된 파수별 흡광도를 실험적으로 측정된 파수별 흡광도에 선 맞춤하여 공기의 밀도가 측정되었다. 부르돈 압력계를 사용하여 기체 챔버 내에 상온과 10~100 kPa 범위 내에서 다양한 압력을 가지는 시험 조건들이 만들어졌다. 삼각 나선 형태의 광경로 및 로그 증폭기를 사용한 흡수 신호 증폭을 통해, 16 %의 오차 이내에서 좁은 시험 구간의 공기 밀도가 측정될 수 있음이 확인되었다.

Keywords

Acknowledgement

본 연구는 방위사업청 산하 국방과학연구소의 선도형 핵심기술(응용연구) 사업에 의한 연구비 지원을 받아 수행된 연구임(No. UC190056CD).

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